refactor(commands): separate commands and its core into two folders (#32)

- I think it would be better if one for commands only, one for the spec
handling core logic so people won't be confused by the core logic inside
the commands folder (cleaner I guess)
- Regen docs

commands/ops/volta.go

@@ -1,14 +1,14 @@
 package ops
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "volta",
 		Description: "Enables verbose diagnostics",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "fetch", Description: "Fetches a tool to the local machine"},
 			{Name: "install", Description: "Installs a tool in your toolchain"},
 			{Name: "uninstall", Description: "Uninstalls a tool from your toolchain"},
@@ -21,7 +21,7 @@ func init() {
 			{Name: "run", Description: "Run a command with custom Node, npm, and/or Yarn versions"},
 			{Name: "help", Description: "Prints this message or the help of the given subcommand(s)"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--verbose", Description: "Enables verbose diagnostics"},
 			{Name: "--quiet", Description: "Prevents unnecessary output"},
 			{Name: "-h", Description: "Prints help information"},